Malaria remains the most important vector-borne disease globally, affecting 300-500 million persons annually. Of the 15 million cases reported from Latin America, more than 50% are from Brazil. In anopheline mosquitoes responsible for malaria transmission, little is known about gene flow, which can provide valuable information about local patterns of dispersal and malaria transmission. Using molecular techniques, this project proposes to elucidate gene flow and population genetics within species of the Anopheles albitarsis complex and An darlingi in Amazonian Brazil. Anopheles darlingi is the most efficient malaria vector in Latin America while species in the An. albitarsis complex have been implicated as important local vectors in Brazil. Both species are in the Argyritarsis Section in the subgenus Nyssorhynchus. Adult mosquitoes will be collected bi-monthly in two adjacent endemic malaria sites in Amapa State in Amazonian Brazil. Mitochondrial DNA haplotype profiles will be analyzed for temporal and microgeographic changes. The effective migration rates (Nem) will be computed using 4 methods. Molecular identification of cryptic species will be coupled with parasite detection by ELISA and dissection. An attempt will be made to link specific haplotypes to infectivity and to evaluate the significance of this for malaria transmission. A PCR-based probe for more rapidly and efficiently identifying vector species will be developed and tested. Mosquitoes will be collected along a transect to examine regional gene flow within species based on biological and ecological differences of Art albitarsis and An. darlingi. A phylogenetic hypothesis for the evolutionary relationships among species in the Argyritarsis Section will be constructed using molecular and morphological data sets.